A diaphragm tank 12 for potable water typically has a metal shell 22 and a plastic liner 24 (FIG. 1). A diaphragm 26 is mounted below the liner 24, defining an air cushion between the shell 22 and the diaphragm 26 and an expandable bladder enclosed by diaphragm 26 and liner 24. A gasket 28 is usually mounted around the hole between the shell 22 and the liner 24 to stiffen the metal shell 22 and plastic liner 24 in the area of the hole and to form an airtight seal to block the leakage of air (FIG. 2).
A connector 10 is mounted on diaphragm tank 12 to allow fluid to flow into or out of the tank (FIG. 1). Connector 10 extends through both the shell 22 and the liner 24. A conventional connector includes a passage fitting 14 and an o-ring 16 mounted around the passage fitting 14 (FIG. 2). The interior end of the passage fitting 14 is bent into a curled end 18 to retain the o-ring 16 on the passage fitting 14. A shoulder 20 abuts the outside of the tank 12, allowing the wall of tank 12 to be clamped between the shoulder 20 and the curled end 18 of the passage fitting 14.
The connector 10 links the tank to a water flow. When the pressure of the flowing water is greater than that of the air cushion, water flows into the bladder. When the water pressure decreases, the pressurized air in the tank expands against the bladder, pushing the water out until the air pressure is the same as the water pressure or the tank is empty.
As shown in FIG. 2, a large force is required to press the curled end 18 around o-ring 16, and curled end 18 will easily be cracked. This reduces the pressure on o-ring 16, reducing its ability to seal the connector 10 and reducing the strength of the passage fitting 14. In addition, the diameter of the contact area between the curled end 18 of the passage fitting 14 and the liner 24 is only slightly larger than the diameter of the hole, allowing a gap to form between liner 24 and gasket 28. This allows air from the tank 12 to enter the water resident in the space between liner 24 and diaphragm 26. Because the air in the tank does not circulate, it may contain harmful bacteria and other microorganisms that could cause disease if air retained in the tank was allowed to mix with the water passing in and out of the bladder. As a result, it is desirable to have a more robust seal between the connector and the remainder of the tank.